1. Field of the Invention
This invention relates to a cylindrical armature or more in particular to a coreless armature in which a rotor cup and a shaft are coupled securely to each other.
2. Description of the Prior Art
In the conventional cylindrical armature of the above-mentioned type, a glass filament impregnated with resin is spirally wound on the whole peripheral surface of a mandrel, thus forming an inner cylindrical insulating layer. On this insulating layer, an armature winding is arranged cylindrically. Another glass filament also impregnated with resin is spirally wound on the whole outer periphery of the armature winding thereby to form an outer cylindrical insulating layer.
As many taps as the coils of the armature winding are taken out at one end of the armature winding and connected to a commutator bar.
After forming the insulating layers on the inner and outer peripheral surfaces of the armature winding, the resin is hardened thereby to form a rotor cup. This rotor cup is securely bonded, by means of a bonding agent and by the use of an appropriate jig, on the outer peripheral surface of a rotor ring already firmly fixed on the shaft.
In such a conventional method, a layer of the bonding agent is unavoidably formed in the junction between the rotor cup and the rotor ring.
The transmission of the torque generated in the rotor cup to the shaft solely depends on the bonding agent between rotor cup and rotor ring. Therefore, the torque transmissibility is determined by the shearing stress of the bonding agent. In actual operation, ambient temperatures are so unfavorable that the differences in the coefficients of thermal expansion of the rotor cup, the rotor ring and the bonding agent cause a thermal stress, thus adversely affecting the bonding strength of the bonding agent.
Further, the fact that the rotor cup formed by hardening resin is bonded to the rotor ring by means of an assemblying jig causes an out-of-alignment situation between the rotor cup and the shaft or the crossing of the axis of the rotor cup with that of the shaft. Such an out-of-alignment or crossing of the axes causes an unbalanced rotation and an increased gap between the armature and the stator, resulting in a deteriorated efficiency.
As will be noted from the above description, the conventional method for bonding the rotor cup to the rotor ring not only lacks the reliability in bonding strength but also deteriorates the quality and electric efficiency of the machine.